A technology called redundant arrays of inexpensive disks (RAID) has been proposed, in which a plurality of storages are combined and operated as a single virtual storage group, thereby improving redundancy. There is another technology in which a modification map that records an updated part of data updated after backup for a plurality of storages is provided and, when reconstructing data of a storage in which a failure has occurred, data in the updated part recorded in the modification map is reconstructed on the basis of data of other storages. Furthermore, there is still another technology in which a plurality of disks and a backup storage used for backup of data of the plurality of disks are provided and, when a faulty disk, among the plurality of disks, is replaced with another disk, data of the replacement disk is recovered from the backup storage.
Japanese Laid-open Patent Publication No. 2002-108571 and Japanese Laid-open Patent Publication No. 2006-252126 disclose related techniques.
However, according to related techniques, in the case where a failure has occurred in a storage of a storage group, if, while rebuilding processing of recovering the redundancy of the storage group is performed, a failure occurs in another storage of the storage group, it may be difficult to recover the storage group.